It is well known that a conventional railway car truck comprises a pair of wheel-supported side frames, with a car-supporting bolster extending between the side frames. The ends of the bolster are slidably mounted in large openings or windows in the side frames, and each bolster end is resiliently supported upon a plurality of spring groups or coils in respective side frames. Depending on whether the railway or car is loaded, the bolster spring groups or coils are relatively compressed or extended.
Many arrangements have been proposed for providing proper spring support for the bolster and car body to satisfy both loaded and unloaded conditions. In accordance with one proposal, one or more of the outer coils may be shorter than the inner coils, such that the outer coil is not compressed under unloaded conditions but is engaged and provides resilient support when the car is loaded. In order to prevent this shorter coil from tilting to the side and interfering with adjacent springs during an unloaded conditions, it is known to dispose a small diameter coil within the short coil. The inner coil is longer than the short coil and extends fully between the bolster and side frame under unloaded conditions in order to retain the short coil in position.
It has been found that when a two stage spring as described above is employed, some means must be provided to retain or hold the lower end of the inner coil relative to the outer coil; otherwise, the outer coil will tilt sufficiently to interfere with the inner coil or another adjacent coil. The lack of a suitable retaining means has discouraged the extensive use of such two stage springs by the industry.